1. Field of the Invention
The present invention relates to a device for identifying line reversal/ringing signals of a telephone set, more particularly, to an identifying device for discriminating the line reversal signal and the ringing signal of the telephone set without using a CPU installed in the telephone set.
2. Description of Related Art
Currently, a telephone set or an answering machine usually with a function of discriminating a caller's ID has a built-in CPU to support main and additional functions. The CPU is transferred to a sleep mode to save power when the telephone set is not in use. A conventional method to identify a signal transmitted on line utilizes the CPU of the telephone set in cooperation with a built-in ringing detection circuit thereof to determine if the signal is a line reversal signal or a ringing signal. However, by such a method, the CPU must be transferred from the sleep mode to an operation mode, so that the load of the CPU is increased and excessive power is consumed.
Another conventional method utilizing a timer, which involves use of a clock signal, also consumes a lot of power.